CHICAGO -- Longtime tea-drinking may strengthen bones, researchers in Taiwan have found.
The benefits occurred in people who drank an average of nearly two cups daily of black, green or oolong tea for at least six years, said the researchers from National Cheng Kung University Hospital in Tainan, Taiwan.
Their results are published in the May 13 edition of Archives of Internal Medicine.
The findings could have broad public health implications, because fractures associated with bone-thinning osteoporosis and low bone density are a global problem expected to worsen with the predicted increase in the number of older people worldwide.
Some estimates suggest nearly half the U.S. population aged 50 and older is affected by osteoporosis or low bone mass, and the World Health Organization projects that the number of hip fractures could rise from 1.7 million in 1990 to 6.3 million by 2050.
Tea contains fluoride and chemical compounds known as flavenoids that include estrogen-like plant derivatives -- both of which may enhance bone strength, the authors said.
Their study is based on surveys of 1,037 men and women aged 30 and older who were questioned about tea-drinking habits and had bone-mineral density tests. The researchers accounted for other factors affecting bone strength, including gender, age, body-mass index and lifestyle.
About half the participants were habitual tea drinkers -- those who routinely drink tea for at least one year. Most of the habitual tea drinkers consumed green or oolong tea without milk, which contains bone-building calcium.
Both varieties are more commonly consumed in Asia, while black tea is more common in Western countries.
All three come from the same plant but are processed differently.
The highest overall bone-mineral density was found in people who said they had consumed tea regularly for more than 10 years; their hip-bone density was 6.2 percent higher than in non-habitual tea drinkers.
Habitual drinkers for six to 10 years had a hip-bone density 2.3 percent higher than in non-habitual tea drinkers, said Dr. Chih-Hsing Wu, a co-author.
There were no significant differences between tea drinkers of one to five years and non-habitual drinkers. Similar results were found regardless of type of tea consumed.
Previous research on tea-drinking and bone strength is limited and has been mixed.
The varying findings ''may result from different study designs ... inconsistent definition of tea intake categories, and incomplete adjustment of the confounding effects of lifestyle characteristics such as exercise, alcohol intake'' and smoking, Dr. Chih-Jen Chang and colleagues wrote.
Dr. Meir Stampfer of Harvard's School of Public Health called the results interesting but far from proof that tea strengthens bones.
''It may be other characteristics of tea drinkers'' that explain the bone mineral density differences, said Stampfer, who was not involved in the research.
''I would not recommend changes in tea consumption based on the results of this study,'' he said.
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